I don't know about in the UK, but here in the US, that wouldn't be legit. Finding the music and/or the lyrics to project on a screen is not the hard part. Any modern worship song is copy-written and trademarked and the church entity needs to be licensed to use it in a service. A church is a business like any other, albeit not-for-profit, and still needs to follow the same copyright and trademarked laws.
That aside, just having the OS, office, and A/V (and any other software) installed does not mean it is licensed, and even if it is, more often than not, software licenses aren't transferable. If a church entity wants to do things right, this is not the way to go.